It takes some time for a withdrawal application to be withdrawn. If you didn't get a response from IRCC saying that they had received your application to withdraw, then they haven't received it or acted on it yet.
You need to contact IRCC now and let them know you have decided to withdraw. Call them. Email them. Raise a webform. Without an acknowledgement from them, attend the interview and tell them that you are withdrawing your sponsorship.
It is essential you get an acknowledgement from them that you are withdrawing.